AGK, along with the sphingosine (SPHK1, 2) and ceramide (CERK) kinases and the ceramide kinase like protein (CERKL), comprise the sphingolipid kinase family. AGK is unique among members of this family in that it is a mitochondrial protein. We discovered that mice lacking a functional AGK allele die early in embryogenesis due to failure to implant, which is also unlike SPHKs, CERK or CERKL where null mice are viable and fertile. However, the lipid substrate of phosphoryl transfer reaction catalyzed by AGK is uncertain. The research program we propose will discover that substrate/product and in doing so will define a lipid metabolic pathway that is most likely crucial to mitochondrial survival. Specifically, we will: (Aim 1) Generate matched pairs of cell cultures and tissues wherein AGK expression is markedly different and use mass spectrometry to characterize the lipidome of those cells and tissues so as to ultimately identify the reaction catalyzed by AGK and (Aim 2) characterize AGK function in mitochondria by determining its sub- organelle location, studying mitochondrial physiology in cells deficient in AGK and using conditional deletion of AGK alleles to determine the fate of cell lineages in the mouse. Our extensive experience studying lysophospholipid chemical biology including sphingosine kinases coupled with expertise in mitochondrial physiology will enable us to solve this problem. Minimally, the experiments proposed will reveal a new branch of sphingolipid metabolism. Maximally, we will define a new pathway that is integral to mitochondrial function. PUBLIC HEALTH RELEVANCE: A number of serious pathologies are characterized by defects in the body's energy factories, which are cell organelles named mitochondria. Depending on the organ system affected in mitochondrial diseases, symptoms might include poor growth, muscle weakness, diabetes, neurological problems such as seizures, respiratory disorders and dementia. In this project, we study a protein named AGK, which is thought to be involved in lipid metabolism. AGK is a mitochondrial protein and we discovered that mice lacking this protein die early in embryo formation, which indicates that AGK is essential for development in mammals including humans. We are researching AGK to learn the nature of the lipid pathway that is affected by AGK and why this pathway is so important to mitochondrial survival. Our intention is to use this knowledge to provide better understanding, diagnosis and, eventually, treatment of mitochondrial disease.